Methods and apparatus for determining the location of a shaft within a vessel

ABSTRACT

Apparatus and methods for measuring the amount by which the centerline of a shaft disposed in a vessel is offset from the central vertical axis of the vessel, and for measuring the height of such shaft above the inside bottom of the vessel. Apparatus includes a shaft centerline offset measurement device, a shaft height measurement device, and a control/display console. Each measurement device includes a transducer or optical encoder for sensing a displaced position of a biased plunger to which a code strip is mounted. The devices may be combined into a single shaft offset and height measurement device. Improved methods include calculating shaft offset based on a plurality of readings from the transducer, and applying trigonometric relationships. The apparatus and methods are particularly useful in the verification of paddle or basket shafts utilized in dissolution testing stations, so that the dissolution testing protocol complies with government agency guidelines.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of co-pending U.S. patent applicationSer. No. 09/432,704 filed Nov. 2, 1999, the contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention generally relates to measurement of the distanceof a shaft from the bottom of a vessel and the amount by which the shaftis offset from the center of the vessel. More particularly, the presentinvention relates to the precise measurement of shaft height and shaftoffset in vessels employed in dissolution testing systems.

BACKGROUND ART

In the pharmaceutical industry, dissolution testing and analysis isrequired to be performed on samples taken from batches of tablets orcapsules manufactured by pharmaceutical companies in order to assessefficacy and other properties. Dissolution analysis by automated meanshas become popular for increasing throughput and improving accuracy,precision, reliability, and reproducibility. Automation also relievesthe tedium of manually performing a variety of requisite procedures,including: handling and delivering dosage units such as capsules andtablets; monitoring dissolution system parameters; manipulating theshafts carrying the agitation paddles or sample baskets; recording,displaying and printing accumulated data and test results; and cleaningand filtering the vessels employed in such procedures.

Despite the benefits accruing from automation, validation of theprocedures employed in dissolution testing and analysis remains acritical consideration. A typical dissolution test requires, among otherthings, that a rotatable shaft equipped with a paddle or basket beproperly positioned in the center of, and properly located a specifieddistance from the bottom of, a dissolution test vessel prior toconducting the test. The USP has promulgated guidelines for thepharmaceutical industry which are enforced by the FDA. Under USP 24,General Chapters, Dissolution (711), the shaft must be positioned suchthat its centerline is not more than 2 mm at any point from the verticalaxis of the vessel, and such that the paddle or basket (typicallymounted to the lower end of the shaft) be positioned at 25 mm±2 mm fromthe bottom of the vessel.

Various hand-held devices have been utilized to carry out themeasurements required to determine whether a shaft is positioned in adissolution test vessel in compliance with the above-cited guidelines.Rulers, machinist calipers and micrometers, and pass/fail fixturestypify such devices and are known to persons skilled in the art. It isreadily apparent to such skilled persons that operation of these devicesrequires a great deal of manual handling, with critical specificationslargely determined by sight and feel. Conventional shaft measurementdevices therefore engender an unacceptably high risk of error. Thereaccordingly exists a long felt need for improved apparatus and methodsfor determining the position of a shaft installed in the vessel of adissolution testing station.

DISCLOSURE OF THE INVENTION

In accordance with the present invention, an apparatus is mountable to ashaft disposed within a vessel and is adapted for measuring themagnitude by which the centerline of the shaft is offset from thecentral axis of the vessel. The apparatus comprises a housing and aplunger slidably mounted to the housing. The plunger has an outersection extending radially outwardly beyond a wall of the housing, andmeans such as a spring for biasing the plunger radially outwardly. Atransducer is operatively mounted to the housing. The transducer isadapted to encode positions of the plunger and to produce an electricalsignal proportional to a change in position resulting from displacementof the plunger. Means such as data lines are provided for transferringthe signal to means such as a microprocessor for interpreting thesignal.

In another embodiment according to the present invention, an apparatusis mountable to a shaft having a paddle or basket disposed within avessel. The vessel has a central axis and a hemispherical end region.The apparatus is adapted for measuring the distance from a distalsurface of the paddle or basket to a lowermost point on the insidesurface of the hemispherical end region. The apparatus comprises ahousing and a plunger slidably mounted to the housing. The plunger hasan outer section extending outwardly beyond a wall of the housing, andmeans such as a spring for biasing the plunger outwardly. An end portionextends transversely from the plunger beneath the housing and issubstantially centered about a central portion of the housing. Atransducer is operatively mounted to the housing. The transducer isadapted to encode positions of the plunger and to produce an electricalsignal proportional to a change in position resulting from displacementof the plunger. Means such as data lines are provided for transferringthe signal to means such as a microprocessor for interpreting thesignal.

In another embodiment according to the present invention, a system isprovided for determining the location of a rotatable shaft in relationto a vessel mounted to a rack of a dissolution testing station. Theshaft has a first end mounted to the testing station above the vessel, asecond end disposed within the vessel and an operative component securedto the second end. The system comprises a housing including means suchas a resilient clip and groove for removably mounting the housing to theshaft, and a plunger slidably mounted to the housing. The plunger has anouter section extending radially outwardly beyond a wall of the housingand extendable to an inside lateral surface of the vessel, and has meanssuch as a spring for biasing the plunger radially outwardly. Atransducer is operatively mounted to the housing. The transducer isadapted to encode positions of the plunger, and to produce an electricalsignal proportional to a distance from a reference position to anextended position at which the plunger is in contact with the insidelateral surface of the vessel. Means such as data lines are provided fortransferring the signal to means such as a microprocessor forinterpreting the signal.

In another embodiment according to the present invention, a system isprovided for determining the location of a rotatable shaft in relationto a vessel. The vessel has a central axis and a hemispherical endregion, and is mounted to a rack of a dissolution testing station. Theshaft has a first end mounted to the testing station above the vessel, asecond end disposed within the vessel and an operative component such asa paddle or basket secured to the second end. The system comprises aspherical object removably disposed in a lowermost point on an insidesurface of the hemispherical end region of the vessel. A housingincludes means such as a resilient clip or groove for removably mountingthe housing to the shaft. A plunger is slidably mounted to the housing.The plunger has an outer section extending beyond a wall of the housingand extendable to the spherical object, and has means such as a springfor biasing the plunger outwardly. An end portion has an upper surfaceand a lower surface, and extends transversely from the plunger andbetween the operative component and the spherical object.

A transducer is operatively mounted to the housing. The transducer isadapted to encode positions of the plunger, and to produce an electricalsignal proportional to a distance from a reference position at which thetop surface of the end portion of the plunger is biased against theoperative component to an extended position at which the lower surfaceis in contact with the spherical object. Means such as data lines areprovided for transferring the signal to means such as a microprocessorfor interpreting the signal.

In another object according to the present invention, a system isprovided for determining the location of a shaft in relation to a vesselin which the shaft is disposed. The vessel has a central axis and ahemispherical end region. The system comprises a shaft offsetmeasurement device which includes a first housing and a first plungerslidably mounted to the first housing. The first plunger has an outersection extending radially outwardly beyond a wall of the first housingand means such as a spring for biasing the first plunger radiallyoutwardly. A first transducer is operatively mounted to the firsthousing. The first transducer is adapted to encode positions of thefirst plunger and to produce a first electrical signal proportional to achange in position resulting from displacement of the first plunger.

The system further comprises a shaft height measurement device whichincludes a second housing and a second plunger slidably mounted to thesecond housing. The second plunger has an outer section extendingoutwardly beyond a wall of the second housing, and means such as aspring for biasing the second plunger outwardly. An end portion extendstransversely from the second plunger beneath the second housing and issubstantially centered about a central portion of the second housing. Asecond transducer is operatively mounted to the second housing. Thesecond transducer is adapted to encode positions of the second plungerand to produce a second electrical signal proportional to a change inposition resulting from displacement of the second plunger.

The system further comprises a console including logic means such as amicroprocessor for effecting interpretations of the first and secondelectrical signals and means such as an LCD display for displaying theinterpretations in human-readable form. Means such as data lines areprovided for transferring the first and second electrical signals to thelogic means.

In another embodiment according to the present invention, an apparatusis adapted for measuring the magnitude by which the centerline of ashaft is offset from the central axis of a vessel in which the shaft isdisposed, and for measuring the distance from a distal end of the shaftto the lowermost point on an inside surface of a hemispherical endregion of the vessel. The apparatus comprises a mounting assembly, alateral plunger slidably mounted to the mounting assembly, a lateraltransducer operatively disposed with respect to the mounting assemblyand to the lateral plunger, a vertical plunger slidably mounted to themounting assembly, and a vertical transducer operatively disposed withrespect to the mounting assembly and to the vertical plunger.

The lateral plunger has means such as a spring for biasing the lateralplunger radially outwardly. The lateral transducer is adapted to encodepositions of the lateral plunger and to produce an electrical signalproportional to a change in position resulting from displacement of thelateral plunger. The vertical plunger has means such as a spring forbiasing the vertical plunger downwardly with respect to the mountingassembly, and includes an upper end portion extending transversely fromthe vertical plunger. The vertical transducer is adapted to encodepositions of the vertical plunger and to produce an electrical signalproportional to a change in position resulting from displacement of thevertical plunger. Means such as data lines are provided for transferringthe signals produced respectively by the lateral and verticaltransducers to means for interpreting the signals. The signalinterpreting means can include a console with which the signaltransferring means communicates, wherein the console has logic meanssuch as a microprocessor for effecting interpretations of the signalsand means such as an LCD display for displaying the interpretations inhuman-readable form.

The present invention also provides methods for determining the positionof a shaft installed in a vessel with respect to the central axis of thevessel and/or lowermost point inside the vessel.

Accordingly, a method is provided for measuring the amount by which thecenterline of a shaft is offset from the central axis of a vessel inwhich the shaft is to be disposed, comprising the following steps. Ameasurement device which includes a radially outwardly biased plunger ismounted to the shaft. The plunger has a settable zero referenceposition. The shaft is inserted into the vessel at a normal operatingposition of the shaft, wherein a distal end of the plunger is in contactwith a lateral inside surface of the vessel at a first distal plungerposition. A first displaced plunger position is defined as a position onthe plunger located a distance by which the plunger has moved inrelation to the zero reference position, the distance being equal afirst displacement magnitude.

The displacement magnitudes are measured by encoding the displacedplunger position and interpreting the displaced plunger position inrelation to the zero reference position, wherein the displacementmagnitudes determine the shaft centerline offset amount. A value for theshaft centerline offset amount is calculated based on the measured firstdisplacement magnitudes. Finally, a signal is produced which isindicative of the shaft centerline offset amount.

Accordingly, another method is provided wherein a distal end of theplunger position is in contact with a lateral inside surface of thevessel at a first distal plunger position. This first displaced plungerposition is reset to the zero reference position. The shaft is thenrotated one full revolution while continuously sampling the displacementof the plunger position is defined as a position on the plunger locateda distance by which the plunger has moved in relation to the zeroreference position, the distance being equal to the displacementmagnitude from this continuous sampling, the lowest and the largestdisplacement magnitudes are kept.

Another method according to the present invention is for measuring ashaft height, which is defined as the distance between the distal end ofa shaft and the inside lowermost surface of a hemispherical end regionof a vessel in which the shaft is to be disposed. The method comprisesthe following steps. A measurement device which includes a downwardlybiased plunger is mounted to the shaft. The plunger includes an endportion. The end portion extends below the shaft and has a predeterminedend portion height. A zero reference position of the plunger is definedby urging the end portion against the distal end of the shaft. The zeroreference position is encoded. The inside lowermost surface of thehemispherical end region of the vessel is located by inserting aspherical object having a predetermined diameter into the vessel. Theshaft is inserted into the vessel at a normal operating position of theshaft, permitting the end portion of the plunger to contact thespherical object.

A displaced plunger position is defined as a position on the plungerlocated a distance by which the plunger has moved in relation to thezero reference position in order to contact the spherical object, thedistance being equal to a displacement magnitude. The displacementmagnitude is measured by encoding the displaced plunger position andinterpreting the displaced plunger position in relation to the zeroreference position, wherein the sum of a predetermined constant plus thedisplacement magnitude is proportional to the shaft height. A value forthe shaft height is calculated based on the measured displacementmagnitude. A signal is produced which is indicative of the shaft height.

A further method according to the present invention is for measuring theamount by which the centerline of a shaft is offset from the centralaxis of a vessel in which the shaft is to be disposed, and for measuringa shaft height defined as the distance between the distal end of theshaft and the inside lowermost surface of a hemispherical end region ofthe vessel. The method comprises the following steps. The insidelowermost surface of the hemispherical end region of the vessel islocated by inserting a spherical object into the vessel. A measurementdevice is mounted over the vessel. The measurement device includes alateral plunger and a vertical plunger. The vertical plunger includes anend portion. The shaft is inserted into the vessel at a normal operatingposition of the shaft.

A distal end of the lateral plunger is permitted to contact a lateralinside surface of the vessel. A displaced lateral plunger position isdefined as a position on the lateral plunger located a lateral distanceby which the lateral plunger has moved in relation to a predeterminedzero reference position of the lateral plunger, the lateral distancebeing equal to a lateral displacement magnitude. The lateraldisplacement magnitude is measured by encoding the displaced lateralplunger position and interpreting the displaced lateral plunger positionin relation to the zero reference position of the lateral plunger,wherein the lateral displacement magnitude determines the shaftcenterline offset amount. A value for the shaft centerline offset amountis calculated based on the measured lateral displacement magnitude. Asignal is produced which is indicative of the shaft centerline offsetamount.

The end portion of the vertical plunger is permitted to contact thespherical object. A displaced vertical plunger position is defined as aposition on the vertical plunger located a vertical distance by whichthe vertical plunger has moved in relation to a predetermined zeroreference position of the plunger, the vertical distance being equal toa vertical displacement magnitude. The vertical displacement magnitudeis measured by encoding the displaced vertical plunger position andinterpreting the displaced vertical plunger position in relation to thezero reference position of the vertical plunger, wherein the verticaldisplacement magnitude determines the shaft height. A value for theshaft height is calculated based on the measured vertical displacementmagnitude. A signal is produced which is indicative of the shaft height.

It is therefore an object of the present invention to provide anapparatus for measuring the amount by which the centerline of a shaftdisposed in a vessel is offset from the central vertical axis of thevessel.

It is another object of the present invention to provide an apparatusfor measuring the height of such shaft above the lowermost inside pointof the vessel.

It is a further object of the present invention to provide an apparatusfor controlling the process by which the shaft centerline offset amountand shaft height are measured, and for expressing the results of suchprocess using peripheral devices.

It is yet another object of the present invention to provide improvedmethods for determining accurate values for the shaft centerline offsetamount and shaft height.

Some of the objects of the invention having been stated hereinabove,other objects will become evident as the description proceeds, whentaken in connection with the accompanying drawings as best describedhereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a paddle shaft installed in a vesselin which the present invention is implemented;

FIG. 2 is a perspective view of a dissolution testing station in whichthe present invention is implemented;

FIG. 3A is a perspective view of a shaft centerline offset and heightmeasurement system according to the present invention;

FIG. 3B is a perspective view of a shaft height measurement deviceaccording to the present invention;

FIG. 3C is a perspective view of a shaft centerline offset measurementdevice according to the present invention;

FIG. 4A is a front elevation view of the shaft centerline offsetmeasurement device in FIG. 3C;

FIG. 4B is a rear elevation view of the shaft centerline offsetmeasurement device in FIG. 3C;

FIG. 4C is a top plan view of the shaft centerline offset measurementdevice in FIG. 3C;

FIG. 4D is a bottom plan view of the shaft centerline offset measurementdevice in FIG. 3C;

FIG. 5A is a front elevation view of the shaft height measurement devicein FIG. 3B;

FIG. 5B is a rear elevation view of the shaft height measurement devicein FIG. 3B;

FIG. 5C is a top plan view of the shaft height measurement device inFIG. 3B;

FIG. 5D is a bottom plan view of the shaft height measurement device inFIG. 3B;

FIGS. 6A and 6B are front and rear elevation views, respectively, of ashaft centerline offset measurement device mounted to a shaft within avessel according to the present invention;

FIGS. 7A and 7B are front and rear elevation views, respectively, of ashaft height measurement device mounted to a shaft within a vesselaccording to the present invention;

FIGS. 8A, 8B and 8C are geometric views illustrating a method forcalculating the offset amount of the centerline of a shaft according tothe present invention;

FIG. 9 is a geometric view illustrating another method for calculatingthe offset amount of the centerline of a shaft according to the presentinvention;

FIGS. 10A and 10B are perspective views of a combined shaft centerlineoffset and height measurement device according to the present invention;

FIGS. 11A and 11B are detailed perspective views of a shaft centerlineoffset measurement module of the device in FIGS. 10A and 10B;

FIG. 12 is a detailed perspective view of a shaft height measurementmodule of the device in FIGS. 10A and 10B; and

FIGS. 13A and 13B are a flow diagram of a test routine according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a typical vessel V employed in a dissolution testingstation, while FIG. 2 illustrates one such testing station generallydesignated DTS. Vessel V has an open upper end 12, a lateral side region14, and a hemispherical end region 16. A plurality of vessels V(typically 6 or 8) are mounted in a rack 18 of dissolution testingstation DTS for high-throughput testing. Each vessel V is centered andlocked into position on rack 18 with the aid of a vessel centering ringCR (not shown in FIG. 2). Dissolution testing station DTS includes,among other components, a water bath WB for temperature control ofvessels V and a programmable systems control module 20 having peripheralelements such as an LCD display 20A, a keypad 20B, and individualreadouts 20C. A shaft S provided with a paddle or basket P may beinserted into each vessel V. One or more spindle motors (not shown)housed within control module 20 drive the rotation of shafts S through achuck (not shown) or equivalent coupling means. Referring specificallyto FIG. 1, the parameters of shaft position relative to vessel V soughtto be determined are shaft centerline offset determined by shaftdistance x, and shaft or paddle height y. The present inventiondescribed in detail below has been found by applicants to measure theseparameters accurately to within 0.1 mm.

FIGS. 3A through 3C show a shaft centerline offset and heightmeasurement system according to the present invention and generallydesignated 30. Primary components of measurement system include a shaftcenterline offset measurement device generally designated 40, a heightmeasurement device generally designated 50, and a control/displayconsole generally designated 60. Control/display console 60 is portableand thus includes a handle 60A. A keypad 60B is provided for inputtingcommands, calibration data, and the like. Results derived frommeasurements taken by centerline offset and height measurement devices40, 50 are transferred through electrical conduits EC and may bedisplayed at display screen 60C, which is preferably an LCD typedisplay. Alternatively, these results may be sent through acommunication port 60D such as an RS 232 port to another peripheral suchas a remote computer. Control/display console 60 can also be equippedwith an on-board dot-matrix printer 60E. In addition, control/displayconsole 60 includes a decoder chip adapted for decoding signal receivedfrom transducers, a CPU for performing calculations and other computingfunctions, a memory register, and other associated logic components andcircuitry (not shown). A suitable decoder chip is a quadrature decoderavailable from HEWLETT PACKARD as model designation HCTL-2016. Asuitable CPU is a micro controller unit available from PHILLIPS as modeldesignation 87C52.

Centerline offset measurement device 40 is illustrated in more detail inFIGS. 3C and 4A through 4D. Height measurement device 50 is illustratedin more detail in FIGS. 3B and 5A through 5D.

Referring particularly to FIGS. 3C and 4A, centerline offset measurementdevice 40 includes a housing 42, a lateral plunger 44, and ahorizontally-oriented sensor or transducer 46(indicated schematically inFIG. 4A by phantom lines). Preferably, both lateral plunger 44 andtransducer 46 are mounted within housing 42. Lateral plunger 44 ismovably mounted to housing 42 by conventional means, such that lateralplunger 44 can slide inwardly and outwardly with respect to housing 42.An outer section 44A of lateral plunger 44 extends outside housing 42through a hole 42A in a wall 42B of housing 42. Means such as a spring(not shown) is provided to interface with lateral plunger 44 and housing42 and to impart a biasing force to lateral plunger 44 in a radiallyoutward direction away from housing 42. Preferably, an arrow-shapedplunger head 44B is provided at a distal end 44C of lateral plunger 44for a purpose described hereinbelow. Means such as an electrical conduitEC containing lead wires is provided for transferring signals generatedby transducer 46.

Transducer 46 serves to measure a change in lateral position of lateralplunger 44 by converting a sense of the physical change in such positionto an electronic signal representative of the magnitude of such change.For this purpose, transducer 46 is preferably an optical linear encodermodule such as model designation HEDS 9200 R00 available from HEWLETTPACKARD. Transducer 46 operates in conjunction with a code strip (notshown) in a manner typical of optical encoders. Because transducer 46 isto measure positional changes of lateral plunger 44, the code strip ismounted to an inner section 44D of lateral plunger 44 in the vicinity oftransducer 46. Hence, as lateral plunger 44 moves, the code strip moveswith respect to transducer 46. As the code strip passes by transducer46, transducer 46 optically reads and counts lines on the code strip.The number of lines counted is correlated to a magnitude by whichlateral plunger 44 has moved from an initial reference position.Alternatively, transducer 46 could be mounted to lateral plunger 44 andthe code strip fixedly secured within housing 42.

Referring to FIGS. 3C, 4B and 4C, a longitudinal recess 48 is formed ina rear face 42C of housing 42 by a recess wall 48A. Preferably, recesswall 48A has a cylindrical profile to better accommodate the contour ofshaft S. In an upper section 48B of longitudinal recess 48 proximate toa top face 42D of housing 42, a clip-like member 49 is provided toassist the secure mounting of shaft centerline offset measurement device40 to shaft S. Clip-like member 49 includes a pair of resilient prongs49A and 49B. In addition, a bottom face 42E of housing 42 may beconfigured to conform to the specific type of operative component, e.g.,paddle or basket P, carried on shaft S in order to further assist inmounting thereto. Thus, in the exemplary embodiment shown in FIG. 4D,bottom face 42E includes a groove 42F that enables housing 42 tostraddle paddle P when mounted to shaft S. FIGS. 6A and 6B showcenterline offset measurement device 40 mounted to shaft S and shaft Sinstalled in vessel V.

Referring particularly to FIGS. 3B and 5A, height measurement device 50includes a housing 52, a vertical plunger 54, and a vertically-orientedsensor or transducer 56 (indicated schematically in FIG. 5A by phantomlines). As in the case of centerline offset measurement device 40, bothvertical plunger 54 and transducer 56 are preferably mounted withinhousing 52. Vertical plunger 54 is movably mounted to housing 52 byconventional means, such that vertical plunger 54 can slide inwardly andoutwardly with respect to housing 52. An outer section 54A of verticalplunger 54 extends outside housing 52 through a hole 52A in a wall 52Bof housing 52. Means such as a spring (not shown) is provided tointerface with vertical plunger 54 and housing 52 and to impart abiasing force to vertical plunger 54 in a downward direction away fromhousing 52. An end portion 54B is attached to vertical plunger 54 inoffset relation thereto by means of an intermediate member 54C.Accordingly, when height measurement device 50 is mounted to shaft S,vertical plunger 54 is situated in parallel relation to shaft S and endportion 54B is centrally disposed beneath shaft S and its operativecomponent P. The purpose of end portion 54B is described hereinbelow.Finally, means such as an electrical conduit EC containing lead wires isprovided for transferring signals generated by transducer 56.

In a manner analogous to that respecting centerline offset measurementdevice 40, transducer 56 serves to measure a change in vertical positionof vertical plunger 54 by converting a sense of the physical change insuch position to an electronic signal representative of the magnitude ofsuch change. Consequently, transducer 56 specified for heightmeasurement device 50 is the same or similar unit as transducer 46specified for centerline offset measurement device 40, as well as theassociated code strip which preferably is mounted to vertical plunger54.

Referring to FIGS. 3B, 5B and 5C, means are provided for mounting heightmeasurement device 50 to shaft S similar to that respecting centerlineoffset measurement device 40. That is, a longitudinal recess 58 isformed in a rear face 52C of housing 52 by a cylindrically-profiledrecess wall 58A. A clip-like member 59 including a pair of resilientprongs 59A and 59B is disposed in an upper section 58B of longitudinalrecess 58 proximate to a top face 52D of housing 52. In addition, abottom face 52E of housing 52 includes a groove 52F or other means forimproving the securement of height measurement device 50 to shaft Sprovided with paddle P or the like, as shown in FIG. 5D. FIGS. 7A and 7Bshow height measurement device 50 mounted to shaft S and shaft Sinstalled in vessel V.

The operation of shaft centerline offset and height measurement system30 will now be described with particular reference to FIGS. 3A, 6A, 6B,7A, 7B, 8A through 8C, and 9. By way of example, an indication ofcenterline offset is obtained before an indication of shaft or paddleheight is obtained.

Referring to FIGS. 6A and 6B, the operation of centerline shaftmeasurement device 40 will first be described. Centerline offsetmeasurement device 40 is affixed to shaft S. Shaft S is then loweredinto vessel V at a normal operating position for shaft S. Becauselateral plunger 44 is preferably biased radially outwardly, the taperededges that comprise arrow-shaped plunger head 44B assist in installingand removing shaft S from vessel V when centerline offset measurementdevice 40 is mounted to shaft S. After shaft S is disposed in its normaloperating position, a distal end (which in the present exemplaryembodiment corresponds to the outermost surface of plunger head 44B) ofoutwardly biased lateral plunger 44 is in contact with a lateral insidesurface ID of vessel V.

At this point, assuming shaft S is offset from the true central verticalaxis of vessel V, lateral plunger 44 will have displaced laterally withrespect to a zero reference position. At this plunger position, lateralplunger 44 will have displaced a distance equal to a displacementmagnitude. This displacement magnitude is evident by the change inposition of the code strip mounted to lateral plunger 44. Transducer 46encodes the displaced position of the code strip, and thus the displacedposition of lateral plunger 44, and sends the encoded signal tocontrol/display console 60 (see FIG. 3A), which decodes, stores, andprocesses the signal.

The displacement magnitude measured is one indication of the amount bywhich shaft S is offset from the central axis of vessel V. Thisdisplacement magnitude alone, however, is not necessarily a goodindication when one considers that the position of lateral plunger 44will change when lateral plunger 44 is disposed at other distal plungerpositions on the circumference of lateral inside surface ID of vessel V.Accordingly, more precision can be achieved by employing transducer 46to sample a plurality of displaced plunger positions. These displacedplunger positions are obtained when lateral plunger 44 is rotated todefine a plurality of distal plunger positions located on thecircumference of lateral inside surface ID. By doing so, a calculationof the centerline offset amount can be based on a plurality ofdisplacement magnitudes measured by transducer 46 at differentcircumferential locations on lateral inside surface ID.

Referring to FIGS. 8A through 8C, lateral inside surface ID is assumedto be a perfect circle ABC for purposes of calculation and has a centerO through which central axis of vessel V runs. The centerline of theshaft S is represented by a point T, thus illustrating that shaft S isclearly not in alignment with the central axis of vessel V. Shaft S withcenterline offset measurement device 40 mounted thereto is inserted intovessel V as described above, at which time distal end or plunger head44B of lateral plunger 44 contacts lateral inside surface ID at a firstdistal plunger position A. The distance by which lateral plunger 44 isdisplaced at this time is encoded by transducer 46 and stored incontrol/display console 60 as a first displacement magnitude. After thefirst displacement magnitude is measured, second and third displacementmagnitudes are likewise measured by respectively rotating lateralplunger 44 120° (or one-third of a revolution around lateral insidesurface ID) to a second distal plunger position B and another 120° to athird distal plunger position C.

Lateral plunger 44 can be rotated by manually rotating housing 42 aroundshaft S or by rotating shaft S itself. In order to aid in locating the120° positions, indicator marks (not shown) could be provided, forinstance, on vessel centering ring CR (see FIG. 1). Nevertheless, themethod described herein will give an accurate indication of centerlineoffset even if readings are taken at plunger positions that deviateapproximately ±5° from the 120° positions.

Referring to FIG. 8A, a radial distance d₁, along lateral plunger 44from centerline T to first distal plunger position A, a radial distanced₂ along lateral plunger 44 from centerline T to second distal plungerposition B, and a radial distance d₃ along lateral plunger 44 fromcenterline T to third distal plunger position C are obtained. Radialdistances d₁, d₂ and d₃ can be derived in a variety of ways, such as bytaking a value representing some constant plunger length and adjustingthat value by taking into account the measured first, second and thirddisplacement magnitudes, respectively. A chordal distance AB betweenfirst and second distal plunger positions A, B, a chordal distance ACbetween first and third distal plunger positions A, C and a chordaldistance BC between second and third distal plunger positions B, C arethen calculated respectively according to the following equationsderived from the law of cosines:${AB} = \sqrt{\left( d_{1} \right)^{2} + \left( d_{2} \right)^{2} - {2 \cdot d_{1} \cdot d_{2} \cdot {\cos \left( {\frac{2 \cdot \pi}{360} \cdot 120} \right)}}}$${AC} = \sqrt{\left( d_{1} \right)^{2} + \left( d_{3} \right)^{2} - {2 \cdot d_{1} \cdot d_{3} \cdot {\cos \left( {\frac{2 \cdot \pi}{360} \cdot 120} \right)}}}$${BC} = \sqrt{\left( d_{3} \right)^{2} + \left( d_{2} \right)^{2} - {2 \cdot d_{3} \cdot d_{2} \cdot {\cos \left( {\frac{2 \cdot \pi}{360} \cdot 120} \right)}}}$

Next, a theoretical radius R for circle ABC based on chordal distancesAB, AC, and BC is calculated according to the following equation:$R = \frac{{AB} \cdot {AC} \cdot {BC}}{4 \cdot \sqrt{S \cdot \left( {S - {AB}} \right) \cdot \left( {S - {AC}} \right) \cdot \left( {S - {BC}} \right)}}$${{wherein}\quad {factor}\quad S} = \frac{{AB} + {AC} + {BC}}{2}$

Referring to FIG. 8B, it follows that radius R is equal to a radius AOfrom center O to first distal plunger position A, a radius BO fromcenter O to second distal plunger position B, and a radius CO fromcenter O to third distal plunger position C. An angle AOB between radiiAO and BO is then calculated according to the following equation derivedfrom the law of cosines:${AOB} = {{\cos^{- 1}\left( \frac{({AO})^{2} + ({BO})^{2} - ({AB})^{2}}{{2 \cdot {AO} \cdot {BO}}\quad} \right)} \cdot \frac{360}{2 \cdot \pi}}$

Referring to FIG. 8C, values for radial distances AT and BT are equal toradial distances d₁ and d₂, respectively. Thus, an angle ABT betweenradial distances AT and BT is calculated according to the followingequation derived from the law of sines:${ABT} = {{\sin^{- 1}\left( \frac{d_{1} \cdot {\sin \left( \frac{120 \cdot 2 \cdot \pi}{360} \right)}}{AB} \right)} \cdot \frac{360}{2 \cdot \pi}}$

Next, an angle ABO between chordal distance AB and radius BO and anangle OBT between radius BO and radial distance BT are calculatedaccording to the following equations: ${ABO} = \frac{180 - {AOB}}{2}$OBT = ABT − ABO

It will be seen from FIG. 8C that a triangle is defined by threevertices corresponding to center O, centerline T, and second distalplunger position B. Because the values for two sides of this triangle,radius BO and radial distance BT, and the angle OBT therebetween areknown, control/display console 60 can now calculate the value for theremaining side, which is the offset distance OT of centerline T fromcenter O. Offset distance OT is calculated according to the followingequation derived from the law of cosines:${OT} = \sqrt{({BO})^{2} + \left( d_{2} \right)^{2} - \left( {2 \cdot {BO} \cdot d_{2} \cdot {\cos \left( \frac{{OBT} \cdot 2 \cdot \pi}{360} \right)}} \right)}$

The offset distance OT provides an accurate indication of the amount bywhich the centerline of shaft S is offset from the central axis ofvessel V in any radial direction. This is because the calculation isbased on three displacement magnitudes measured at three differentpositions of lateral plunger 44 within vessel V, and the relationshipsbetween the various points and distances observed within vessel V anddescribed hereinabove can be resolved by trigonometric equations.

A preferred modification to the method described above yields the sameresult, i.e., calculation of offset distance OT, yet avoids theadditional task of deriving values for radial distances AT, BT and CTfrom the first, second and third displacement magnitudes. In thispreferred modification, advantage is taken of the fact that the first,second and third displacement magnitudes measured by transducer 46 arelinearly proportional to radial distances AT, BT and CT, respectively.Thus, radial distance d₁ is set equal to zero, radial distance d₂ is setequal to a value based on the second displacement magnitude relative tothe first displacement magnitude, and radial distance d₃ is set equal toa value based on the third displacement magnitude relative to the firstdisplacement magnitude. For example, d₁=0, d₂=−0.1, and d₃=−0.9. If suchvalues for d₁, d₂ and d₃ are used and the above equations applied, thesame value for offset distance OT is obtained.

A further alternative method for calculating the amount by which thecenterline of shaft S is offset from the central axis of vessel V willnow be described with reference to FIG. 9. Lateral inside surface ID ofvessel V is represented by a circle AB in FIG. 9, and has a center Othrough which the central axis of vessel V runs. The centerline of shaftS is represented by point T. If a diameter for circle AB is drawnthrough center O and centerline T, it is observed that a maximumdisplacement magnitude will be measured when lateral plunger 44 isdisposed within vessel V along a maximum radial distance AT, and aminimum displacement magnitude will be measured when lateral plunger 44is rotated 180° and disposed along a minimum radial distance BT. Iflateral inside surface ID of vessel V were a perfect circle, an offsetdistance OT could be found by subtracting radius AO from radial distanceAT or by subtracting radial distance BT from radius BO. A preferredmethod of calculation, however, is derived as follows.

It is observed that maximum radial distance AT=AO+OT and minimum radialdistance BT=BO−OT. For purposes of calculation, lateral inside surfaceID of vessel V is assumed to be a perfect circle such that AO=BO. Thus,minimum radial distance BT=AO−OT. Offset distance OT can be found bysubtracting maximum radial distance AT from minimum radial distance BTas follows:

AT−BT=(AO+OT)−(AO−OT)=2OT

Therefore,${OT} = {\frac{\left( {{AO} + {OT}} \right) - \left( {{AO} - {OT}} \right)}{2} = \frac{{AT} - {BT}}{2}}$

In order to implement this method, lateral plunger 44 is rotated 360°,i.e., one full revolution around the inside of vessel V. Atpredetermined intervals while lateral plunger 44 is rotating, e.g.,every 5 ms, transducer 46 encodes the position of lateral plunger 44 togenerate a data set consisting of a plurality of displacementmagnitudes. From this data set, a maximum measured displacementmagnitude d_(MAX) and a minimum measured displacement magnitude d_(MIN)are selected. An example of a subroutine that could perform thisselection process can be constructed from the following steps:

1) READ a first displacement magnitude and STORE;

2) READ a second displacement magnitude and STORE;

3) IF second displacement magnitude<first displacement magnitude, THENSET second displacement magnitude=d _(MIN) AND SET first displacementmagnitude=d_(MAX), ELSE SET second displacement magnitude=d_(MAX) ANDSET first displacement magnitude=d_(MIN);

4) READ a third displacement magnitude;

5) IF third displacement magnitude<d_(MIN) THEN SET third displacementmagnitude=d_(MIN);

6) IF third displacement magnitude>d_(MAX) THEN SET third displacementmagnitude=d_(MAX).

This procedure is repeated successively until each sampled displacementmagnitude is determined to be either the maximum or minimum for the dataset. Offset distance OT is then calculated according to the followingequation: ${OT} = \frac{d_{MAX} - d_{MIN}}{2}$

Referring primarily to FIGS. 7A and 7B, the operation of heightmeasurement device 50 will now be described. Height measurement device50 is affixed to shaft S. Prior to installation of shaft S in vessel V,a spherical object such as a stainless steel ball 65 having apredetermined uniform diameter is placed into vessel V. Stainless steelball 65 will come to rest at a lowermost point 19 on the inside surfaceof hemispherical end region 16 of vessel V, thereby locating the truebottom of vessel V. Vertical plunger 54 is biased to a fully downwardlyextended position. In order to obtain a zero reference position, endportion 54B of vertical plunger 54 is urged upwardly until good contactis made with the underside of paddle P or other operative component ofshaft S. Shaft S is then inserted into vessel V at a normal operatingposition for shaft S.

Once shaft S has been installed, vertical plunger 54 moves downwardlyuntil coming into contact with stainless steel ball 65. At this point,vertical plunger 54 will have displaced vertically with respect to thezero reference position. The distance by which vertical plunger 54displaces is characterized as its displacement magnitude. Transducer 56encodes the displaced position by reading the code strip mounted tovertical plunger 54 and generates a signal representative of themeasured displacement magnitude, in a manner analogous to theinteraction of transducer 46 and the code strip of lateral plunger 44 ofcenterline offset measurement device 40 described hereinabove.Transducer 56 sends the encoded signal to control/display console 60(see FIG. 3A). The height of paddle P above lowermost point 19 ofhemispherical end region 16 is most easily derived from the measureddisplacement magnitude by adding together the values for thedisplacement magnitude, the height of end portion 54B and the diameterof stainless steel ball 65.

As an alternative embodiment of the present invention, shaft centerlineoffset and height measurement system 30 can be modified to incorporateboth the shaft centerline offset and height measurement functions in asingle measurement device. That is, housing 42 or 52 can be adapted toaccommodate both transducers 46 and 56, plungers 44 and 54, and theirassociated components described hereinabove. However, a preferredapproach to this functional combination is to provide a more modulardevice which does not require the mounting of a single (and bulkier andheavier) housing to shaft S.

This preferred alternative embodiment will now be described withreference to FIGS. 10A, 10B, 11A, 11B and 12, illustrating a combinedshaft centerline offset and height measurement device generallydesignated 70.

Instead of employing a housing to serve as a mounting assembly forcentralizing the operative components of the present embodiment, amodified vessel centering ring 75 is provided. Modified vessel centeringring 75 includes a central region 75A having a bore 75B through whichshaft S with paddle P or the like can be inserted.

Combined shaft centerline offset and height measurement device 70includes a centerline offset measurement module generally designated 80and a height measurement module generally designated 90. It will benoted that all operative components of combined shaft centerline andoffset measuring device 70, including centerline offset measurementmodule 80 and a height measurement module 90, are mounted directly orindirectly to modified vessel centering ring 75, and thus operateindependently of shaft S. Thus, while only one centerline offsetmeasurement module 80 could be provided and rotated by means such as aturntable mounted to modified vessel centering ring 75, it is moreadvantageous to provide three centerline offset measurement modules 80,all of which are suspended from modified vessel centering ring 75independently of shaft S. Moreover, as shown in FIGS. 10A and 10B,centerline offset measurement modules 80 are oriented 120° from eachother, thereby eliminating the alignment and rotation steps attendingcenterline offset measurement device 40 in FIGS. 4A through 4D.

Referring to FIGS. 11A and 11B, each centerline offset measuring module80 includes a sensor body 82 which serves as a mounting bracket for alateral plunger 84 and a transducer 86. Sensor body 82 preferably has aU-shaped profile defined by a central region 82A and legs 82B and 82C.Transducer 86 is preferably secured directly to the inside of leg 82B ofsensor body 82, and preferably is an optical linear encoder similar totransducers 46 and 56. An upper linear bearing 102A is attached to a topsurface 82D of central region 82A and a lower linear bearing 104A isattached to an end 82E of leg 82C. A lower bearing track 104B isattached to each lateral plunger 84 and engages lower linear bearing104A, thereby enabling lateral plunger 84 to slide laterally withrespect to sensor body 82. A code strip 106 is fixedly secured tolateral plunger 84 to cooperate with transducer 86 in the mannerdescribed hereinabove.

As shown in FIG. 10B, three upper bearing tracks 102B (of which only twoare shown) are attached to central region 75A of modified vesselcentering ring 75. Upper linear bearing 102A of each sensor body 82engages a corresponding upper bearing track 102B to enable each sensorbody 82 to slide laterally with respect to modified vessel centeringring 75. In the exemplary embodiment shown in FIGS. 10A and 10B, meanssuch as springs (not shown) are provided respectively for biasing eachlateral plunger 84 radially inwardly and for biasing each sensor body 82radially outwardly. Thus, when shaft S is installed into vessel V,plunger tips 84A of lateral plungers 84 are biased to contact shaft Swhile rear faces 82F of sensor bodies 82 are biased to contact lateralinside surface ID of vessel V. Each lateral plunger 84 has upper andlower guide members 84B and 84C, respectively, to assist in urginglateral plungers 84 outwardly when shaft S is being inserted and removedfrom vessel V.

FIG. 12 is a detailed view of height measurement module 90, which is analternative to incorporating the structure of height measurement device50 described hereinabove. Height measurement module 90 includes a sensormounting bracket 92, a vertical plunger 94, and a vertically-orientedtransducer 96. Vertical plunger 94 preferably includes a vertical rail94A, an upper arm 94B, and a lower arm 94C. Sensor mounting bracket 92includes a clamping section 92A by which sensor mounting bracket 92 isfixedly secured to vertical rail 94A, such as by inserting vertical rail94A through clamping section 92A and tightening clamping section 92Awith a fastener (not shown) threaded into holes 92B.

In the preferred embodiment, lower arm 94C includes an arcuate section94CA and a lower end portion 94CB extending horizontally from arcuatesection 94CA. Likewise, upper arm 94B includes an arcuate section 94BAand a lower end portion 94BB extending horizontally from arcuate section94BA. Arcuate sections 94BA and 94CA are disposed adjacent to eachother, and upper end portion 94BB is disposed above lower end portion94CB. Means such as a spring 98 is connected between upper end portion94BB and lower end portion 94CB in order to vertically bias upper andlower end 94BB and 94CB portions away from each other.

Lower arm 94C is secured to sensor mounting bracket 92, or preferably issecured directly to vertical arm 94A such as by inserting vertical arm94A into an upper portion of lower arm 94CC and employing fasteningmeans similar to clamping section 92A. Upper arm 94B is mounted to anannular bearing 99 through which vertical rail 94A extends, thusenabling upper arm 94B to move vertically with respect to lower arm 94Cand transducer 96. Vertical rail 94A is provided with a longitudinalgroove 94A′ which engages a complementary tongue (not shown) disposedwithin annular bearing 99, thereby preventing annular bearing 99 andupper arm 94B from rotating around vertical rail 94A. Upper arm 94Bincludes a recessed area 94BC into which a code strip (not shown) isattached to cooperate with transducer 96.

Vertical rail 94A is movably attached to modified vessel centering ring75 in order to render combined shaft centerline offset and heightmeasurement device 70 compatible with vessels V of different sizes.Preferably, an annular bearing (not shown) similar to annular bearing 99is attached to modified vessel centering ring 75 and vertical rail 94Ais extended therethrough. In addition, means such as a spring (notshown) is provided to bias vertical rail 94A (and thus heightmeasurement module 90 in its entirety) downwardly.

To complete the measurement system, it will be readily apparent thatcombined shaft centerline and offset measurement device 70 is operablein conjunction with control/display console 60 in FIG. 3A, although somereprogramming is necessary. Combined shaft centerline and offsetmeasurement device 70 can be made to communicate with control/displayconsole 60 by running appropriate data lines such as conduits EC fromtransducers 86, 96 to control/display console 60.

The operation of combined shaft centerline and offset measurement device70 will now be described. Stainless steel ball 65 is inserted intovessel V in order to locate lowermost point 19 of hemispherical endregion 16. Modified vessel centering ring 75, equipped with combinedshaft centerline and offset measurement device 70, is then fitted ontorack 18 of dissolution testing station DTS over one of vessels V. Atthis time, rear face 82F of radially outwardly biased sensor body 82 ofeach centerline offset measurement module 80 makes contact with lateralinside surface ID of vessel V. Additionally, lower end portion 94CB ofdownwardly biased vertical plunger 94 of height measurement module 90makes contact with stainless steel ball 65.

Shaft S is then lowered into vessel V to its normal operating position.Shaft S passes through bore 75B of modified vessel centering ring 75while being lowered into vessel V. Also, paddle P contacts one or moreupper guide members 84B of lateral plungers 84 while shaft S is beinglowered into vessel V, thus urging one or more of lateral plungers 84outwardly to clear the way for paddle P to pass downwardly. Once shaft Sreaches its normal operating position, plunger tips 84A of radiallyinwardly biased lateral plungers 84 are in full contact with shaft S.

Assuming shaft S is offset from the central axis of vessel V, one ormore of lateral plungers 84 of centerline offset measurement modules 80will have displaced outwardly with respect to a predetermined zeroreference position for displaced lateral plunger or plungers 84. Hence,lateral plungers 84 operate in a manner analogous to lateral plunger 44of centerline offset measurement device 40. Each lateral plunger 84 ifdisplaced will have moved by a distance equal to a displacementmagnitude along the radial direction of that particular lateral plunger84. This physical event is measured and converted into an electricalsignal by the coaction of transducer 86 and its associated code strip106 as described hereinabove. Accordingly, three signals representingthe displacement magnitudes at the 120° positions along lateral insidesurface ID of vessel V are sent to control/display console 60. Offsetdistance OT is then preferably calculated by employing the sequence ofsteps including the trigonometric equations described hereinabove.

Height measurement module 90 also operates when shaft S is installed invessel V. Before the bottom end of shaft S or its paddle P reaches itslowermost position within vessel V, upper end portion 94BB of upper arm94B of vertical plunger 94 is biased in its highest position above lowerend portion 94CB of lower arm 94C. This constitutes a zero referenceposition for vertical plunger 94. As shaft S is being lowered intovessel V, paddle P makes contact with upper end portion 94BB. By thetime shaft S reaches its final, normal operating position, paddle P willhave urged upper end portion 94BB downwardly towards lower end portion94CB against the biasing force of spring 98. As the code strip forvertical plunger 94 is fixedly mounted in recessed area 94BC of upperarm 94B, the code strip moves downwardly by the same distance as upperend portion 94BB. This distance constitutes the displacement magnitudefor vertical plunger 94, which is encoded by transducer 96, and a signalis sent to control/display console 60 for further processing. One way toderive or interpret the height of paddle P above lowermost point 19 ofvessel V is to add together values for the measured displacementmagnitude, the height of upper end portion 94BB, the height of lower endportion 94CB, and the diameter of stainless steel ball 65.

It will be understood that while the Figures depict control/displayconsole 60 as being portable and designed for remote operation, thepresent invention encompasses a variation wherein control/displayconsole 60 is integrated into dissolution testing station DTS. Forexample, the operative components of control/display console 60 can behoused within programmable systems control module 20 of dissolutiontesting station DTS (see FIG. 2).

FIGS. 13A and 13B illustrate by way of example a flow diagram of a testroutine executable by software written for control/display console 60.The particular test routine illustrated manages the operation of shaftcenterline offset and height measurement system 30 with centerlineoffset measurement device 40 and height measurement device 50. It willbe understood, however, that the software can be rewritten without undueexperimentation and adapted for use of control/display console 60 withcombined shaft centerline offset and height measurement device 70. It isalso to be noted that this test routine can be configured, for example,to test up to 30 dissolution testing stations DTS and up to 8 shafts Sand corresponding vessels V per dissolution testing station DTS.Therefore, a total of 240 shaft sites can be tested in a single testroutine if desired.

Referring again to FIGS. 13A and 13B, display screen 60C ofcontrol/display console 60 displays a main menu at step 115, promptingthe user to select either a test run for shaft height measurement or atest run for shaft offset measurement. If the user selects a test runfor shaft height measurement, a shaft height measurement subroutine120-137 is initiated. On the other hand, if the user selects a test runfor shaft offset (or “ctr line”) measurement, a shaft offset measurementsubroutine 140-157 is initiated.

When the shaft height measurement subroutine is initiated, the user isprompted at step 120 to assign an integer from 1 to 30 to thedissolution testing station presently being tested in order todistinguish that testing station from other testing stations to betested. The user is then prompted at step 125 to input an identificationfor that particular testing station, such as a serial number. Shaftsoperating in that testing station are assigned numbers according to therespective positions of the shafts in the testing station, such as 1through 6 or 1 through 8. Thus, the user is prompted at step 130 toeither initiate testing of a particular shaft, proceed to the nextshaft, or exit the shaft height measurement subroutine and return to themain menu.

If the user desires to test that particular shaft, the user is promptedat step 131 to input an identification for the shaft, such as a serialnumber. Next, the user is prompted at step 132 to input anidentification for the vessel in which the shaft operates. The user isthen prompted to place the stainless steel ball into the vessel at step133, install the shaft height measurement device at step 134, press thevertical plunger upwardly against the paddle or basket of the shaft inorder to obtain a zero reference reading at step 135, and lower theshaft equipped with the height measurement device into the vessel atstep 136. Once the shaft height measurement has been taken andappropriately interpreted, a readout or indication of the shaft heightis displayed at step 137 and the user is prompted to test another shaftin the particular testing station being tested.

When the shaft centerline offset measurement subroutine is initiated byselection at step 115, the user is prompted at step 140 to assign aninteger to the dissolution testing station presently being tested. Theuser is then prompted at step 145 to input an identification for thatparticular testing station. Next, the user is prompted at step 150 toeither initiate testing of a particular shaft identified by its positionnumber, proceed to the next shaft, or exit the shaft centerline offsetmeasurement subroutine and return to the main menu.

If the user desires to test that particular shaft, the user is promptedat step 151 to input an identification for the shaft. Next, the user isprompted at step 152 to input an identification for the vessel in whichthe shaft operates. The user is then prompted to install the shaftcenterline offset measurement device at step 153, and to lower the shaftequipped with the offset measurement device into the vessel at step 154.After a key input is entered at this position, the user is prompted atstep 155 to rotate the shaft 120°. A key input is requested to indicatethe completion of this step. The user is then prompted at step 156 torotate the shaft another 120°, and a key input is requested to indicatethe completion of this step. Once the measurements taken at thesepositions have been appropriately interpreted and the offset distancecalculated, a readout or indication of the shaft centerline offset isdisplayed at step 157 and the user is prompted to test another shaft inthe particular testing station being tested.

These steps are repeated for every shaft and dissolution testing stationdesired by the user to be tested.

It will be understood that in the case where the centerline offset ismeasured by making one full rotation around the vessel in order tosample a plurality of displacements, the steps of the test routine aremodified accordingly. It will also be understood that in the case wherea testing routine such as that just described is adapted for use inconjunction with combined shaft centerline offset and height measurementdevice 70, the total number of steps required by the test routine can bereduced.

It will be further understood that various details of the invention maybe changed without departing from the scope of the invention.Furthermore, the foregoing description is for the purpose ofillustration only, and not for the purpose of limitation—the inventionbeing defined by the claims.

What is claimed is:
 1. An apparatus mountable to a shaft having a paddleor basket disposed within a vessel, the vessel having a central axis anda hemispherical end region, the apparatus adapted for measuring thedistance from a distal surface of the paddle or basket to a lowermostpoint on the inside surface of the hemispherical end region andcomprising: (a) the housing comprising a rear face, a top face, and acoupling component for coupling the housing to the shaft, the couplingcomponent comprising a longitudinal recess and a clip, wherein thelongitudinal recess is defined by a recess wall extending inwardlytoward an interior of the housing from the rear face, the longitudinalrecess comprises an upper section extending downwardly from the topface, the upper section has a width greater than a width of an adjacentsection of the longitudinal recess, and the clip extends outwardly fromthe recess wall within the upper section and comprises a pair ofresilient prongs; (b) a plunger slidably mounted to the housing, theplunger having an outer section extending outwardly beyond a wall of thehousing, means for biasing the plunger outwardly, and an end portionextending transversely from the plunger beneath the housing andsubstantially centered about a central portion of the housing; (c) atransducer operatively mounted to the housing and adapted to encodepositions of the plunger and to produce an electrical signalproportional to a change in position resulting from displacement of theplunger; and (d) means for transferring the signal away from thehousing.
 2. The apparatus according to claim 1 wherein the longitudinalrecess and the prongs cooperatively define a cylindrical profile.
 3. Theapparatus according to claim 1 further comprising a plate mounted to theplunger and including a plurality of equally spaced lines readable bythe transducer, wherein the transducer is an optical encoder disposedwithin the housing and the number of lines read by the transducercorresponds to a magnitude of the change in position of the plunger. 4.The apparatus according to claim 1 wherein the signal transferring meansincludes an electrical conduit.
 5. The apparatus according to claim 1wherein the clip defines a cross-sectional area disposed in substantialaxial alignment with a cross-sectional area of the longitudinal recess.6. The apparatus according to claim 1 comprising a device forinterpreting the signal, the device disposed remotely in relation to thehousing and communicating with the signal transferring means.
 7. Theapparatus according to claim 6 wherein the signal interpreting devicecomprises a display component for displaying the interpreted signal inhuman-readable form.
 8. An apparatus mountable to an elongate memberdisposed within a vessel and adapted for determining the position of anend of the elongate member in relation to a lowermost point on theinside surface of the vessel, the apparatus comprising: (a) a housingdisposed along a longitudinal axis and comprising a clip device forcoupling the housing to the elongate member; (b) a plunger movablymounted to the housing and linearly displaceable inwardly toward andoutwardly from the housing along a direction substantially parallel tothe longitudinal axis; (c) a transducer supported by the housing inoperative relation to the plunger and adapted for sensing a displacementof the plunger and for producing an electrical signal indicative of thedisplacement of the plunger; and (d) an electrical conduit communicatingwith the transducer for conducting the signal produced by thetransducer.
 9. The apparatus according to claim 8 wherein the plungerincludes a plunger arm and an end portion, the plunger arm is mounted tothe housing and linearly displaceable inwardly toward and outwardly fromthe housing along a direction substantially parallel to the longitudinalaxis, and the end portion extends transversely from the plunger armbeneath the housing and is generally centered in relation to a centralregion of the housing.
 10. The apparatus according to claim 9 whereinthe housing includes a longitudinal recess formed in an outer surface ofthe housing, and the end portion of the plunger is generally alignedwith the longitudinal recess.
 11. The apparatus according to claim 8wherein the housing includes a longitudinal recess formed in an outersurface of the housing and operatively aligned with the clip device. 12.The apparatus according to claim 8 wherein the housing comprises a topface and a longitudinal recess defined by a recess wall extendinginwardly toward an interior of the housing, the longitudinal recesscomprises an upper section extending downwardly from the top face, andthe clip device is disposed within the upper section.
 13. The apparatusaccording to claim 8 wherein the clip device comprises a pair ofresilient prongs.
 14. The apparatus according to claim 13 wherein eachprong has an inside surface, and the clip device and inside surfaces ofthe prongs cooperatively define a cylindrical profile.
 15. An apparatusmountable to an elongate member disposed within a vessel and adapted fordetermining the position of an end of the elongate member in relation toa lowermost point on the inside surface of the vessel, the apparatuscomprising: (a) a housing disposed along a longitudinal axis; (b) aplunger comprising an arm and an end portion, wherein the arm is mountedto the housing and is linearly displaceable inwardly toward andoutwardly from the housing along a direction substantially parallel tothe longitudinal axis, and the end portion extends transversely from thearm beneath the housing and is generally centered in relation to acentral region of the housing; (c) a transducer supported by the housingin operative relation to the plunger and adapted for sensing adisplacement of the plunger and for producing an electrical signalindicative of the displacement of the plunger; and (d) an electricalconduit communicating with transducer for conducting the signal producedby the transducer.
 16. The apparatus according to claim 15 wherein thehousing includes a longitudinal recess formed in an outer surface of thehousing, and the end portion of the plunger is generally aligned withthe longitudinal recess.
 17. The apparatus according to claim 16 whereinthe housing includes a coupling element disposed in operative alignmentwith the longitudinal recess and with the end portion.
 18. The apparatusaccording to claim 15 wherein the housing includes a coupling element,and the end portion of the plunger is generally aligned with thecoupling element.
 19. The apparatus according to claim 15 wherein atleast a portion of the arm is disposed within the housing and extendsthrough an opening of the housing.
 20. The apparatus according to claim15 comprising a spring element disposed in biasing engagement with theplunger.
 21. The apparatus according to claim 15 comprising anelectronic circuit communicating with the electrical conduit and adaptedfor receiving the signal conducted by the electrical conduit.
 22. Anapparatus mountable to an elongate member disposed within a vessel andadapted for determining the position of an end of the elongate member inrelation to a lowermost point on the inside surface of the vessel, theapparatus comprising: (a) a housing having a longitudinal axis; (b) aplunger comprising an arm and an end portion, wherein the arm is mountedto the housing and is linearly displaceable inwardly toward andoutwardly from the housing along a direction substantially parallel tothe longitudinal axis, and the end portion extends transversely from thearm beneath the housing and is generally centered in relation to acentral region of the housing; (c) a transducer operatively mounted tothe housing and adapted to encode positions of the plunger and toproduce an electrical signal proportional to a change in positionresulting from displacement of the plunger; and (d) means fortransferring the signal away from the housing; and (e) a device forinterpreting the signal, the device disposed remotely in relation to thehousing and communicating with the signal transferring means.
 23. Theapparatus according to claim 22 wherein the housing comprises a clip forcoupling the housing to the elongate member.
 24. The apparatus accordingto claim 23 wherein the housing comprises a longitudinal recess, and theclip is operatively aligned with the longitudinal recess.
 25. Theapparatus according to claim 23 wherein the clip comprises a pair ofresilient prongs.
 26. The apparatus according to claim 22 wherein thearm is slidably disposed within the housing and extends outwardlythrough a hole in the wall of the housing.
 27. The apparatus accordingto claim 22 wherein the signal transferring means comprises anelectrical conduit.
 28. The apparatus according to claim 22 wherein thesignal interpreting device comprises a display component for displayingthe interpreted signal in human-readable form.